Pathology - Circulation Flashcards
What lines the lumen of blood vessels?
endothelium
What is around the basal lamina of blood vessels?
smooth muscle
What is around the smooth muscle in blood vessels?
interstitial collagen fibres
What does the lumen of blood vessels contains?
- red blood cells
- white blood cells
- platelets
- plasma
What does plasma consist of?
water, proteins, other solutes
What does plasma contain?
clotting factors
Where are many clotting factors mainly produced?
in the liver but also by endothelial cells
What are clotting factors?
an amplification system, resulting in thrombin production
What does thrombin do?
converts soluble fibrinogen into insoluble fibrin
What does fibrin do?
forms a mesh of strands
Simplified clotting cascade
damage → TF + prothrombin → thrombin + fibrinogen → fibrin
What is meant by initial damage in the clotting cascade?
one obvious is trauma
What does trauma lead to?
- exposure of interstitial collagens (collagens in connective tissue between structures)
- exposure of a molecule called tissue factor (TF)
What is tissue factor released from?
smooth muscle
What does “many clotting factors are serine proteases” mean?
that clotting factors have a serine amino acid in them and they cleave other clotting factors to form the active molecule
Where are platelets produced?
in bone marrow from a cell called megakaryocyte
What is a megakaryocyte?
large cell with many nuclei
How do platelets work
trauma to vessel → exposure of platelets to interstitial collagen → platelets adhere together and try to form bridge to close gap
What is coagulation
Solidification of blood (clotting)
What are the 2 types of coagulation
- Thrombus formation
2. Clot formation
Where does thrombus formation occur
In flowing blood
Pure thrombus
- Pale cream coloured
- Consists of platelets and a mesh like network of fibrin strands
What is thrombosis
The process of thrombus formation
Why does a thrombus of platelets and fibrin occur in flowing blood?
platelets have molecules on their surfaces which allows adherence to interstitial collagen ever when blood is flowing past them - the clotting cascade deposits factor VIII which enhances this further
Where does clot formation occur?
Blood leaks out of a vessel and becomes stationary (stagnant)
Describe clot formation
Wishing the stagnant blood, sitting next to interstitial collagen, the clotting cascade is activated
A clot consists of a network of fibrin strands and red blood cells
What is haemostasis
Stopping bleeding
What is the role of vasoconstriction in bleeding
Helps reduce bleeding
How is thrombus removed?
A blood protein called plasminogen converts to plasmin, and plasmin cuts up fibrin into smaller fragments as a way of removing fibrin. In a thrombus this is sometimes called thrombolysis
What does the fibrinolytic system depend on?
- Plasma protein called plasminogen being converted to plasmin
- Plasmin cuts up fibrin into fibrin degradation products
What are the 3 main causes of thrombosis (virchow’s triad)
In the absence of cut or traumatic injury
Example of pathological thrombosis -coronary artery thrombosis
- coronary arteries are the main arteries in the heart and supply the heart muscle
- smoking cigarettes increases the stickiness of platelets (find it easier to aggregate)
- stickier platelet makes it more likely that a thrombosis will occur
- this alteration in the properties of blood is a change in blood constituents which is part of Virchow’s triad
- cigarette smoking can also predispose to atheroma in the coronary arteries
- atheroma can occur and slowed blood flow predisposes to fibrin and platelet clumping - this is an example of a change in the pattern of blood flow which is part of Virchow’s triad
- lipid can also rupture through the intimal surface which is a change in the intimal surface, also part of Virchow’s triad
What is atheroma?
a disease of coronary arteries which results in a build up of lipids under the intimal surface
What can atheroma result in?
the lipid can result in abnormal blood flow - can get both slow and turbulent flow
Lines of Zahn
arterial thrombus - multiple layers of thrombus and clot (pale layers of thrombus alternating with red layers of clot)
What does complete obstruction by thrombus blocking an artery lead to?
No flow beyond the blockage
What does partial obstuction by thrombus blocking an artery lead to?
Decreased blood flow beyond the blockage
What is ischaemia
Poor blood flow
Describe the consequences of ischaemia
- If it is severe enough can lead to decreased oxygenation of tissues
- The tissue is said to be ‘ischaemic’
- Ischaemic heart tissue is often painful
What is hypoxia?
Decreased oxygenation of tissues
What is an infarct?
A localised area of dead tissue as a result of Ischaemia
What is coronary artery thrombosis
Infarct in heart
What is cerebral artery thrombosis
Infarct in brain
What is an embolism
A mass of material moves in the vascular system and bale to become lodged in a vessel and block its lumen
What are most emboli derived from?
Thrombi or clots
What do emboli do?
Break off and go elsewhere in the circulation
What is thromboemolis?
When thrombi/clots embolise
How does a pulmonary embolism occur?
- Sluggish flow in leg veins lead to thrombosis and clot formation
- Part of thrombus breaks off and travels up vein
- Embolus passes into inferior vena cava, then the right heart. then pulmonary artery bench
- Embolism block pulmonary artery and get pulmonary infarct
Provide an example of marrow embolism
fracture a leg -> marrow enters ruptures -> air embolisms to lung vessels
Examples of air embolism
Knife wound to neck -> air enters vein -> marrow embolisms to lung vessels
What is circulatory school?
Profound circulatory failure causing poor perfusion of vital organs
What does shock mean in practice?
Low blood pressure in physiological consequences
What does normal blood pressure rely on?
Enough blood in the system
Smooth muscle in vessels having a certain ‘tone’
heart pumping blood
What is normal blood pressure(arterial)
120/80
What happens if smooth muscle tone is decreased?
The vessel will dilate, if enough vessels new affected then blood pressure may fail
There are ____ carotid bodies and ___ carotid sinuses on either side of the neck
2,2
What do the 2 carotid bodies consist of?
Groups of cells which sense the partial pressure of oxygen
What do the carotid sinuses do if blood pressure drops?
They send nerve signals to the brain stem which then tells the heart to pump harder and faster via nerve signals
What is the physiological response to low blood pressure?
Faster pulse
In practice circulatory shock is present if:
- Low blood pressure combined with fast pulse
What are the 3 main causes of circulatory shock
- hypovolaemic
- septic
- cardogenic
Describe hypovolaemic shock
Low blood pressure reflects severe reduction in amounts of blood in circulation
High pulse reflects physiological response to low blood pressure
Describe some of the complications of shcok
- Decreased perfusion of brain -> initially reversible but then permanent
- Decreased perfusion of kidneys -> initially reversible, then more severe
